Referring to FIGS. 1a-1c, sensor assemblies 100 with foam pads and embedded sensors are used to monitor patients. See, e.g., the InSpectra™ device by Hutchinson Technology shown in FIGS. 1a-1c, or the EQUANOX™ from Nonin Medical Inc. In such devices, a sensor shield is permanently attached to the sensor. The sensor assembly may include a foam piece with an adhesive and a liner; the foam piece may have openings for LEDs and detectors. After use, the entire sensor assembly, including the sensor, is thrown away. Such devices therefore utilize relatively unsophisticated sensor technology, limiting the usefulness and accuracy of the patient monitoring system.